Cellular and molecular effects of resveratrol, piceatannol, pterostilbene, pterostilbene phosphate and trans-stilbene oxide in murine macrophages

Stilbenes are polyphenols found in several plants. Whereas the prototype stilbene resveratrol (RES) possesses antioxidant, anti-inflammatory and anticancer properties, considerably less is known about the pharmacology of structural analogs of RES. Therefore, the present study aimed to investigate the pharmacological effects of several RES analogs including piceatannol (PIC), pterostilbene (TPS), pterostilbene phosphate (TPS-P03) and trans-stilbene oxide (TSO), upon transformed and non transformed macrophages. Four hypotheses were tested. The first one was that RES and its analogs would be cytotoxic to nonstimulated tumor-derived mouse macrophages (RAW 264.7) and primary macrophages (PMs) isolated from C57BL/6 mice. Results from cell viability studies supported this hypothesis in RAW 264.7 cells; however, only TPS exhibited toxicity in PMs. Significant increases in caspase 3/9 activities with RES or TPS in RAW 264.7 cells suggested cell death through apoptosis. The second hypothesis was that stimulation of macrophages with LPS would confer cellular resistance to stilbene toxicity. Among the test stilbenes, RES and TPS were found to be less cytotoxic in LPS stimulated RAW 264.7 macrophages than in control cells and the reduction of cell death was confirmed by a decrease in caspase 3/9 activities, especially caspase 3. The third hypothesis proposed that TPS and PIC would exhibit an anti-inflammatory effect similar to that of RES in RAW 264.7 cells. TPS and PIC were found to be more potent than RES at reducing the release of nitric oxide (NO) and prostaglandin E2 (PGE2). The last hypothesis was that the reduction of LPS induced inflammatory effects by stilbenes in mouse macrophages required Nrf2 and would be attenuated in Nrf2-/- macrophages. Nrf2 is a transcription factor involved in cellular stress responses. The inhibitory effect of TPS, RES and PIC on the production of NO and PGE2 in PMs was found to be dependent upon Nrf2 only at low test concentrations. Overall, TPS, which is known to exhibit a better bioavailability than RES, was found to be a more potent anti-inflammatory agent than the parent compound and is worthy of future study.